NEO-MERCAZOLE

What it is

Neo-Mercazole contains 5 mg of carbimazole as the active ingredient. Neo-Mercazole is an anti-thyroid agent believed to exert its antithyroid effect by blocking the organic binding of iodine through inhibition of the iodination of tyrosine. It is also thought to have some action on peroxidase which is required as a catalyst in the synthesis of thyroxine by the thyroid gland.

Approved indications

— Therapy of hyperthyroidism, including definitive therapy for induction of a permanent remission in either primary or secondary thyrotoxicosis. — Preparation for thyroidectomy. — Use before and after radioactive iodine treatment.

Dosing overview

For adults with mild cases, usual initial dosages are 15 to 20 mg per day in divided doses; for moderate cases, 30 mg per day in divided doses; for severe cases, 40 to 45 mg (up to 60 mg) per day in divided doses, titrated against thyroid function until the patient is euthyroid. When symptoms are controlled, the dosage should be reduced to a maintenance level, which will usually be between 10 and 15 mg daily. Once a remission has been secured, maintenance dosage should be continued for at least 12 months, and up to 2 years of treatment may be required.

Key safety warnings

Fatal cases of agranulocytosis with carbimazole have been reported, and patients should always be warned about the onset of sore throats, bruising or bleeding, mouth ulcers, fever, malaise or other symptoms which might suggest bone marrow depression and should be instructed to stop the medicine and to seek medical advice immediately. Cases of vasculitis resulting in severe complications have been reported in patients receiving carbimazole, including leukocytoclastic cutaneous vasculitis, acute kidney injury and glomerulonephritis, alveolar/pulmonary haemorrhage, CNS vasculitis, and neuropathy, with most cases associated with anti-neutrophilic cytoplasmic antibodies (ANCA)-positive vasculitis. If vasculitis is suspected, discontinue therapy and initiate appropriate intervention. There have been post-marketing reports of acute pancreatitis in patients receiving carbimazole, and in case of acute pancreatitis, carbimazole should be discontinued immediately. Women of childbearing potential have to use effective contraceptive measures during treatment, and the use of carbimazole in non-pregnant women of childbearing potential should be based on individual risk/benefit assessment.

Contraindications

Neo-Mercazole is contraindicated in patients with a previous history of adverse reactions to carbimazole or to any of the excipients in the composition. Neo-Mercazole is contraindicated in retrosternal goitre. Serious pre-existing haematological conditions are a contraindication. Severe hepatic insufficiency is a contraindication. Patients with a history of acute pancreatitis after administration of carbimazole or its active metabolite thiamazole should not receive Neo-Mercazole.

PBS listing

Neo-Mercazole 5 mg tablets are listed on the PBS as 2 items with restricted access at an ex-manufacturer price of A$6.25.

Regulatory history

Neo-Mercazole carbimazole 5 mg tablets (ARTG 194296) were first listed on 23 May 2012.